Sintered alloy for decoration

ABSTRACT

There is disclosed a sintered alloy for decoration comprising 
     2 to 30% by weight of a binding phase comprising one or more elements selected from the group consisting of Fe, Ni, Co, Cr, Mo and W; 
     0 to 10% by weight of a strengthening phase comprising one or more material selected from the group consisting of a metal, an alloy, a metal oxide, a metal nitride and a metal carbide; 
     the balance of a hard phase represented by the formula: 
     
         (Tia, Mb) (Nw, Cx, Oy)z 
    
     (wherein M, A, b, w, x, y and z are defined in the specification); and 
     inevitable impurities. 
     The sintered alloy for decoration according to this invention possesses both a decorativeness suitable for decorative members as well as excellent corrosion resistance and mechanical properties.

BACKGROUND OF THE INVENTION

This invention relates to sintered alloys for decoration, having both decorativeness and wear resistance, suitable for decorative members such as external parts for watches, tiepins, brooches, parts for fishing tackles and so on.

For decorative members that are required to have corrosion resistance and to be scratch proof, sintered alloys utilizing WC, TaC and TiC as base materials have been put to practical use. Among these, the WC base and TaC base sintered alloys are unsuitable for portable decorations on account of high cost and great specific gravity, and they have the defect that they cannot satisfy requirements for decorative effects completely, because of having simple blackish gray colors. In order to improve the decorativeness, steels or sintered alloys coated with TiN and/or TiC have been used. These coated alloys, however, still have disadvantages of impairing decorative value. For exmple, there are disadvantages of tone difference between inside and outside of the coated alloys because of the nonuniformities of coating properties and thickness of coating film which are brought about during manufacturing processes. Further, a great number of sintered alloys including TiN as a main component have been proposed to comprise colored sintered alloy members for decoration, but they are very bad in sintering effect. Since such alloys having poor sintering effect are not suitable for decorative members even if a polishing treatment such as lapping will be undergone. Therefore, they have not been put to practical use yet.

The sintered alloy for decoration according to this invention has now been accomplished in order to overcome the aforementioned drawbacks and problems.

SUMMARY OF THE INVENTION

An object of this invention is to provide a sintered alloy for decoration, having both decorativeness and corrosion resistance, suitable for decorative members.

When a mixed powder compact which comprises a material including, as a main component, TiN in a proportion near to its stoichiometric composition and an iron family element is sintered, the TiN is dissolved in the iron family element to form an iron family solid solution. At that time, Ti atom and N atom in TiN cannot be dissolved in the iron family element with equivalent molar ratio, and 95% or more of the nitrogen is liberated from the mixed powder compact in the form of N₂ gas. Therefore, after a liquid phase has appeared, there occurs the phenomenon that the N₂ gas is retained therein, so that densification of the compacts is remarkably disturbed. Now, investigations have been carried out to prevent the denitrification which results from such a phenomenon, and as a result, the sintered alloy for decoration according to this invention has been completed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The sintered alloy for decoration according to this invention comprises:

2 to 30% by weight of a binding phase comprising one or more elements selected from the group consisting of Fe, Ni, Co, Cr, Mo and W;

0 to 10% by weight of a strengthening phase comprising one or more material selected from the group consisting of a metal, an alloy, a metal oxide, a metal nitride and a metal carbide;

the balance of a hard phase represented by the formula:

    (Tia, Mb) (Nw, Cx, Oy)z

(wherein M is one or more elements selected from the group consisting of Zr, Hf, V, Nb, Ta and Cr; a is an atomic ratio of the Ti; b is an atomic ratio of a metal represented by M; a+b=1; 1≧a≧0.4; 0.6≧b≧0; N is nitrogen; C is carbon; O is oxygen; w, x and y are atomic ratios of the nitrogen, carbon and oxygen, respectively; z is a ratio of non-metallic elements with respect to the metals; w+x+y=1; x+y>0; 1>w≧0.4; 0.5≧x≧0; 0.6≧y≧0; and 0.95≧z≧0.6); and

inevitable impurities.

To obtain, in a sintering process, the effect of improving the acceleration of the sintering function and the denseness of the sintered alloy by lowering a liquid phase-appearing temperature of the binding phase and the effect of improving the strength and hardness of the sintered alloy by producing an intermetallic compound or a solid solution, the above-described alloy according to this invention can include one or more metals selected from the group consisting of P, Al, B, Si, Mn, Ti, Zr, Hf, V, Nb and Ta, alternatively one or more alloys thereof, for the strengthening phase. Thereby, the strengthening phase comprising such a metal or alloy will contribute to the improvement in the strength, scratch proof and corrosion resistance of the sintered alloy. Further, for the purpose of improving the strength and hardness of the sintered alloy by dispersing a material into the binding phase, one or more oxides selected from the group consisting of Al₂ O₃, Y₂ O₃, ZrO₂, MgO, NiO and SiO₂ can be used for the strengthening phase. The strengthening phase containing such an oxide will contribute to the improvement in the strength, scratch proof and corrosion resistance of the sintered alloy. Furthermore, for the purpose of increasing the bond strength between the hard phase and the binding phase by strengthening boundaries between particles of the surrounding phases, one or more nitrides or carbides selected from the group consisting of AlN, Si₃ N₄, BN and Mo₂ C, alternatively one or more double compounds thereof can be used for the strengthening phase. The strengthening phase containing such a material will contribute to the improvement in the strength, scratch proof and corrosion resistance of the sintered alloy.

In the sintered alloy according to this invention, since the TiNz (0.95≧z≧0.6) powder having substoichiometric composition is used as a starting material, there occurs the phenomenon that liberated N₂ gas, which would be exhausted out of the system, inversely nitrogenizes the TiNz powder. As a result, the denitrification which would be brought about during the sintering process of the powder compact including TiN as a main component can be prevented. Moreover, according to this invention, carbon and/or oxygen may be added to the TiNz to produce (Tia, Mb)(Nw, Cx, Oy)z, which increases the effect of preventing the denitrification. And at the same time, densification can be accelerated, and the denseness, strength and hardness of the sintered product can be increased, since the carbide of the metal element which has large valence electron number in (Tia, Mb) (Nw, Cx, Oy)z precipitates in the process of sintering, and the carbide had good wettability with an iron family element. By virtue of the synergistic effect which can be created by the use of the hard phase and the strengthening phase, the strength and hardness of the sintered alloy will be further heightened, whereby there can be obtained the sintered alloy excellent in wear resistance, scratch proof and corrosion resistance.

The sintered alloy for decoration according to this invention can retain the tone of a gold color series with the aid of the hard phase in which the TiNz is mainly included. In this case, as a numerical value of the z of TiNz becomes less than that of its stoichiometric composition, the sintered alloy will change from a gold color toward a light gold color. When there is added to the sintered alloy one or more compounds of TiO, ZrN, HfN, VN, NbN, TaN, CrN, Cr₂ N, TaC and NbC which serve to additionally provide the sintered alloy with a golden tone, the control of the tone can easily be carried out ranging from a profound light gold color to a clear gold color.

The sintered alloy for decoration according to this invention can be obtained in an enough dense state under a pressureless sintering in vacuo or in a non-oxidizing atmosphere. In addition, when it is reheated by a hot isostatic pressing method (HIP), it can be prepared in a much denser and stronger state.

The elements constituting the sintered alloy for decoration according to this invention are numerically restricted for the following reasons:

In the (Tia, Mb) (Nw, Cx, Oy)z, which the hard phase comprises, a metal M other than the Ti has not only the effect of grain size control of the hard phase but also the effect of heightening the strength and hardness of the hard phase. Particularly in the case that the metal M is added in the form of one or more compounds, selected from the group consisting of CrN, ZrN, HfN, VN, NbN, TaN and Cr₂ N, which provide a gold color series, the atomic ratios a and b of the Ti and M can be selected from a wide range to prepare a desired alloy. Although there is not any substantial reason to restrict these atomic ratios, it is necessary to take weight-saving for portability and scratch resistance into consideration, and when there is added thereto a carbide such as ZrC, HfC, VC, NbC, TaC or Cr₃ C₂, tone must also be taken into consideration. Accordingly, these ratios should be set to 1≧a≧0.4 and 0.6≧b≧0. With regard to the non-metallic elements N, C and O, the N can be mainly used for the sake of obtaining a golden sintered alloy, and one or both of the C and O can be used for the acceleration of the sintering effect and the improvement in the scratch proof. However, when an amount thereof is excessive, not only the sintering effect but also the hardness of the sintered alloy will be deteriorated. Accordingly, the ratios w, x and y of the non-metallic elements, N, C and O, should be set to 1>w≧0.4, 0.5≧x≧0 and 0.6≧y≧0. In this case, the carbon C should be added in the form of free carbon rather than a metallic carbide, since the former has a more intensive effect of accelerating the sintering effect than the latter. The ratio z of the non-metallic element to the metallic element must be less than the stoichiometric ratio for the sake of preventing degasification and improving the hardness of the sintered alloy, but when it is too small, an obtained compound will be unstable and the dimensional accuracy of the sintered alloy will be poor. Accordingly, it is concluded that the ratio z should be set to the range of 0.95≧z≧0.6.

An amount of the binding phase depends on a relation between amounts of the hard phase and the strengthening phase, and further on a use of the product. However, when the binding phase is contained in an amount less than 2% by weight, the sintering effect and denseness will degrade, on the contrary, when it is contained in an amount more than 30% by weight, the hardness of the sintered alloy will deteriorate and thus the scratch resistance will be poor. Accordingly, the amount of the binding phase should be within the range of 2 to 30% by weight.

An amount of the strengthening phase depends on the amount of the used binding phase and a usage of the product. When it exceeds 10% by weight, the sintering effect will be decrease and the sintered alloy will be brittle. Accordingly, the amount of the strengthening phase should be set to the range of 0 to 10% by weight.

Now, the sintered alloy for decoration according to the present invention will be described in detail with reference to the examples, as follows:

EXAMPLE 1

TiNz, TiC, TiO, Ti(Nw, Cx)z, Ti(Nw, Oy)z and Ti(Nw, Cx, Oy)z were each blended with a metallic powder of the binding phase in a predetermined proportion, and 2% by weight of paraffin was further added thereto as a lubricant. Each blend thus prepared was ground and mixed in a ball mill in which acetone was used as a solvent. After drying, each resultant mixed powder was compacted at a pressure of 2 t/cm², and was then sintered under a vacuum of 10⁻³ to 10⁻⁴ mmHg and at a given temperature of 1400° to 1600° C. Each sintered alloy was polished by means of a diamond grinding wheel, and it was tested for mechanical properties, tones and corrosion resistance. With regard to the mechanical properties, hardness and transverse rupture strength were measured, and the test of the corrosion resistance was carried out by observing the polished surface of each sample after it was dipped in an artificial sea-water and an artificial sweat at 50° C. for a period of 7 days. Blend composition and sintering conditions of each sample are shown in Table 1, and results of the mechanical properties, tone and corrosion resistance of each sample are presented in Table 2:

                                      TABLE 1                                      __________________________________________________________________________     Sample                           Sintering                                     No. Blend composition (wt. %)    conditions                                    __________________________________________________________________________     1   47.5% TiN.sub.0.85 - 47.5% TiO - 5% Ni                                                                      1500° C. - 1 hr                        2   90% TiN.sub.0.70 - 5% TiO - 5% Ni                                                                           "                                             3   90% TiN.sub.0.70 - 5% TiC - 4.5% Co - 0.5% C                                                                "                                             4   80% TiN.sub.0.70 - 5% TiO - 5% TiC - 5% Ni - 5% Mo.sub.2 C                                                  1450° C. - 1 hr                        5   95% Ti (N.sub.0.95, O.sub.0.05).sub.0.85 - 5% Ni                                                            1500° C. - 1 hr                        6   90% Ti (N.sub.0.80, O.sub.0.20).sub.0.70 - 5% Ni - 5%                                                       1450° C. - 1 hr                        7   80% Ti (N.sub.0.70, O.sub.0.30).sub.0.60 - 10% Ni - 5% Mo - 5%                                              "r                                            8   95% Ti (N.sub.0.95, C.sub.0.05).sub.0.90 - 4.9% Ni - 0.1%                                                   1550° C. - 1 hr                        9   90% Ti (N.sub.0.90, C.sub.0.10).sub.0.75 - 5% Ni - 5%                                                       "                                             10  80% Ti (N.sub. 0.85, C.sub.0.15).sub.0.60 - 10% Ni - 5% Co - 5%                                             1450° C. - 1 hr                        11  95% Ti (N.sub.0.85, C.sub.0.05, O.sub.0.10).sub.0.90 - 4.8% Ni - 0.2%          C                            1500° C. - 1 hr                        12  90% Ti (N.sub.0.70, C.sub.0.10, O.sub.0.20).sub.0.80 - 5% Co - 5%                                           "r                                            13  80% Ti (N.sub.0.65, C.sub.0.05, O.sub.0.30).sub.0.65 - 10% Ni - 5%             Mo.sub.2 C - 5% Cr           1450° C. - 1 hr                        __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________     Mechanical properties                                                          Transverse                                                                     rupture                  Corrosion resistance                                  Sample                                                                             strength                                                                             Hardness       Artificial                                                                               Artificial                                  No. (Kg/mm.sup.2)                                                                        (HRA)                                                                               Tone      sea-water sweat                                       __________________________________________________________________________     1   105   90.5 Reddish gold color                                                                       Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                2   110   90.8 Gold color                                                                               Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                3   115   90.3 Light gold color                                                                         Extremely slightly                                                                       Not color-changed                                                    color-changed                                                                            nor corroded                                4   100   90.2 Reddish light gold                                                                       Not color-changed                                                                        Not color-changed                                          color     nor corroded                                                                             nor corroded                                5   105   91.0 Gold color                                                                               Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                6   110   90.5 Reddish light gold                                                                       Not color-changed                                                                        Not color-changed                                          color     nor corroded                                                                             nor corroded                                7   115   90.0 Light gold color                                                                         Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                8   107   90.6 Gold color                                                                               Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                9   103   90.8 Reddish light gold                                                                       Extremely slightly                                                                       Not color-changed                                          color     color-changed                                                                            nor corroded                                10  117   90.1 Reddish light gold                                                                       Not color-changed                                                                        Not color-changed                                          color     nor corroded                                                                             nor corroded                                11  110   91.2 Gold color                                                                               Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                12  108   91.0 Reddish gold color                                                                       Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                13  115   91.1 Reddish light gold                                                                       Not color-changed                                                                        Not color-changed                                          color     nor corroded                                                                             nor corroded                                __________________________________________________________________________

EXAMPLE 2

ZrN, TaN, TaC, NbC, ZrC, VC, HfN, CrN, (Tia, Mb)Nz, (Tia, Mb) (Nw, Cx)z, (Tia, Mb) (Nw, Oy)z and (Tia, Mb) (Nw, Cx, Oy)z were mixed with the powdery materials which were used in Example 1, in a predetermined proportion, and each sintered alloy was prepared in the same manner as in Example 1. Each sintered sample was then tested for mechanical properties, tone and corrosion resistance as in Example 1. Blend composition and sintering conditions of each sample are shown in Table 3, and the mechanical properties, tone and corrosion resistance of each sample are presented in Table 4:

                                      TABLE 3                                      __________________________________________________________________________     Sample                             Sintering                                   No. Blend composition (wt. %)      conditions                                  __________________________________________________________________________     14  85% TiN.sub.0.70 - 5% ZrN - 5% TiO - 5% Ni                                                                    1550° C. - 1 hr                      15  80% Ti(N.sub.0.8, O.sub.0.2).sub.0.70 - 10% TaN - 5% Ni - 5% Mo.sub.2          C                              1600° C. - 1 hr                      16  81% Ti(N.sub.0.95, O.sub.0.05).sub.0.85 - 2% HfN - 2% Mo.sub.2 C - 5%          VC - 10% Ni                    1550° C. - 1 hr                      17  90% Ti(N.sub.0.80, O.sub.0.20).sub.0.70 - 5% NbC - 4.8% Co - 0.2%                                             "                                           18  80% Ti(N.sub.0.65, C.sub.0.05, O.sub.0.30).sub.0.65 - 10% CrN - 5% Ni          - 5% Cr                        "                                           19  75% Ti(N.sub.0.5, O.sub.0.5).sub.0.75 - 20% (V.sub.0.5, Ta.sub.0.5)C           - 5% Ni                        1500° C. - 1 hr                      20  90% (Ti.sub.0.9, Hf.sub.0.1) (N.sub.0.95, C.sub.0.05).sub.0.70 - 5%            Co - 5% Ni                     "                                           21  90% (Ti.sub.0.9, Ta.sub.0.1) (N.sub.0.8, C.sub.0.1,                            O.sub.0.1).sub.0.70 - 5% Ni - 5% Mo                                                                           "                                           22  95% (Ti.sub.0.9, Zr.sub.0.1) (N.sub.0.8, C.sub.0.1,                            O.sub.0.1).sub.0.80 - 4.7% Ni - 0.3% C                                                                        "                                           23  90% (Ti.sub.0.9, Cr.sub.0.1) (N.sub.0.9, C.sub.0.05,                           O.sub.0.05).sub.0.80 - 5% Ni - 5% Cr                                                                          "                                           __________________________________________________________________________

                                      TABLE 4                                      __________________________________________________________________________     Mechanical properties                                                          Transverse                                                                     rupture                 Corrosion resistance                                   Sample                                                                             strength                                                                             Hardness      Artificial                                                                               Artificial                                   No. (Kg/mm.sup.2)                                                                        (HRA)                                                                               Tone     sea-water sweat                                        __________________________________________________________________________     14  100   90.2 Gold color                                                                              Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 15  105   90.5 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 16  103   91.0 Light gold color                                                                        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 17  100   90.3 Gold color                                                                              Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 18  110   90.5 Light gold color                                                                        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 19  115   91.2 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 20  112   91.1 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 21  108   90.8 Reddish light gold                                                                      Extremely slightly                                                                       Not color-changed                                           color    color-changed                                                                            nor corroded                                 22  117   91.2 Gold color                                                                              Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 23  113   90.4 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 __________________________________________________________________________

EXAMPLE 3

Sample Nos. 1, 5 and 8 sintered in Example 1 and Sample Nos. 15, 19 and 23 sintered in Example 2 were each subjected to an HIP treatment under conditions of 1500 bar and 1350° C., and they were then tested for mechanical properties, tone and corrosion resistance. Test results obtained are shown in Table 5.

                                      TABLE 5                                      __________________________________________________________________________                       Mechanical properties                                                          Transverse                                                                     rupture       Corrosion resistance                           Sample            strength                                                                             Hardness                                                                               Artificial                                                                            Artificial                              No. Sample conditions                                                                            (Kg/mm.sup.2)                                                                        (HRA)                                                                               Tone                                                                              sea-water                                                                             sweat                                   __________________________________________________________________________     24  HIP-treated Sample No. 1                                                                     110   90.5 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                25  HIP-treated Sample No. 5                                                                     115   91.1 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                26  HIP-treated Sample No. 8                                                                     120   90.8 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                27  HIP-treated Sample No. 15                                                                    110   90.6 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                28  HIP-treated Sample No. 19                                                                    120   91.0 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                29  HIP-treated Sample No. 23                                                                    125   90.5 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                __________________________________________________________________________

EXAMPLE 4

TiNz, TiC, TiO, Ti(Nw, Cx)z, Ti(Nw, Oy)z, Ti(Nw, Cx, Oy)z, (Tia, Mb)Nz, (Tia, Mb) (Nw, Cx)z, (Tia, Mb) (Nw, Oy)z and (Tia, Mb) (Nw, Cx, Oy)z were each blended with a metallic powder of the binding phase and a metallic powder of the strengthening phase in a predetermined proportion, and 2% by weight of paraffin was further added thereto as a lubricant. Each blend was ground in a ball mill in which acetone was used as a solvent. After drying, each resultant mixed powder was compacted at a pressure of 2 t/cm², and was then sintered under a vacuum of 10⁻³ to 10⁻⁴ mmHg and at a given temperature of 1400° to 1600° C. As need, each sample was subjected to a solid solution treatment in vacuo at a temperature of 1100° to 1250° C. for a period of 3 hours. Each sintered alloy thus obtained was polished by means of a diamond grinding wheel, and was tested for mechanical properties, tone and corrosion resistance in the same manner as in Example 1. Blend composition, sintering conditions and solid solution treatment conditions of each sample are shown in Table 6, and results of the mechanical properties, tone and corrosion resistance of each sample, which underwent the sintering treatment and the solid solution treatment, are presented in Table 7:

                                      TABLE 6                                      __________________________________________________________________________                                      Solid solution                                Sample                   Sintering                                                                              treatment                                     No. Blend composition (wt. %)                                                                           conditions                                                                             conditions                                    __________________________________________________________________________     30  47% TiN.sub.0.85 - 47% TiO - 5.5% Ni - 0.5% P                                                       1450° C. - 1 hr                                                                 --                                            31  90% TiN.sub.0.70 - 4.5% TiC - 5.3% Ni - 0.1% B -                                                    1500° C. - 1 hr                                                                 --                                                0.1% C                                                                     32  90% Ti(N.sub.0.9, C.sub.0.1).sub.0.75 - 7.9% Ni - 2% Al                                             "       1150° C. - 3 hrs                           0.1% C                                                                     33  90% Ti(N.sub.0.7, O.sub.0.3).sub.0.6 - 8.9% Ni - 1% Si                                              1450° C. - 1 hr                                                                 --                                                0.1% C                                                                     34  90% Ti(N.sub.0.8, O.sub.0.2).sub.0.7 - 7% Ni - 3% Mn                                                1500° C. - 1 hr                                                                 --                                            35  90% Ti(N.sub.0.7, C.sub.0.1, O.sub.0.2).sub.0.8 - 8% Ni - 2%                                        "i      1200° C. - 3 hrs                       36  85% (Ti.sub.0.9, Z.sub.0.1) N.sub.0.85 - 5% TiO - 8% Ni                                             1550° C. - 1 hr                                                                 1150° C. - 3 hrs                           1% Ti - 1% Al                                                              37  75% (Ti.sub.0.8, V.sub.0.2) N.sub.0.75 - 5% TiC - 10% Ni                                            "       --                                                5% Co - 5% Zr                                                              38  80% (Ti.sub.0.7, Ta.sub.0.3) (N.sub.0.9, C.sub.0.1).sub.0.7 - 10% Ni           -                    1500° C. - 1 hr                                                                 --                                                5% Co - 5% V                                                               39  93% (Ti.sub.0.8, Cr.sub.0.2) (N.sub.0.9, O.sub.0.1).sub.0.8 - 5% Co                                 1500° C. - 1 hr                                                                 --                                                1.9% Hf - 0.1% C                                                           40  80% (Ti.sub.0.7, Nb.sub.0.3) (N.sub.0.8, C.sub.0.1,                            O.sub.0.1).sub.0.9 - "       --                                                10% Ni - 5% Mo - 5% Nb                                                     41  90% (Ti.sub.0.8, Zr.sub.0.2) (N.sub.0.8, O.sub.0.2).sub.0.8 - 5% Ni                                 1550° C. - 1 hr                                                                 --                                                2% Cr - 3% Zr                                                              42  89% (Ti.sub.0.5, Zr.sub.0.3, Cr.sub.0.2) N.sub.0.8 - 5% TiO                                         "       --                                                5.5% Ni - 0.4% B - 0.1% C                                                  __________________________________________________________________________

                                      TABLE 7                                      __________________________________________________________________________     Mechanical properties                                                          Transverse                                                                     rupture                  Corrosion resistance                                  Sample                                                                             strength                                                                             Hardness       Artificial                                                                               Artificial                                  No. (Kg/mm.sup.2)                                                                        (HRA)                                                                               Tone      sea-water sweat                                       __________________________________________________________________________     30  106   90.8 Reddish gold color                                                                       Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                31  109   91.1 Gold color                                                                               Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                32  105   91.0 Reddish light gold                                                                       Not color-changed                                                                        Not color-changed                                          color     nor corroded                                                                             nor corroded                                33  110   90.8 Light gold color                                                                         Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                34  108   90.7 Reddish light gold                                                                       Not color-changed                                                                        Not color-changed                                          color     nor corroded                                                                             nor corroded                                35  110   91.3 Reddish gold color                                                                       Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                36  110   90.3 Gold color                                                                               Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                37  115   90.2 Light gold color                                                                         Extremely slightly                                                                       Not color-changed                                                    color-changed                                                                            nor corroded                                38  113   90.4 "         Extremely slightly                                                                       Not color-changed                                                    color-changed                                                                            nor corroded                                39  110   90.6 Gold color                                                                               Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                40  115   90.9 "         Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                41  100   91.0 "         Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                42  107   91.2 "         Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                __________________________________________________________________________

EXAMPLE 5

Each powder of Al₂ O₃, Y₂ O₃, ZrO₂, MgO, NiO and SiO₂ and each of the powdery materials used in Example 4 were blended in a predetermined proportion, and were sintered in the same manner as in Example 4. Samples thus obtained were tested for mechanical properties, tone and corrosion resistance. Blend composition, sintering conditions and solid solution treatment conditions of each sample are shown in Table 8, and test results of the mechanical properties, tone and corrosion resistance regarding samples which underwent the sintering treatment and the solid solution treatment are presented in Table 9:

                                      TABLE 8                                      __________________________________________________________________________                                          Solid solution                            Sample                       Sintering                                                                              treatment                                 No. Blend composition (wt. %)                                                                               conditions                                                                             conditions                                __________________________________________________________________________     43  85% TiN.sub.0.85 - 5% TiO - 8% Ni - 1% Y.sub.2 O.sub.3 - 1%                                             1600° C. - 1 hr                                                                 1150° C. - 3 hrs                   44  80% Ti(N.sub.0.9, C.sub.0.1).sub.0.75 - 10% Ni - 5% Co                                                  1550° C. - 1 hr                                                                 "                                             2% MgO - 1% Al - 2% Ti                                                     45  90% Ti(N.sub.0.5, C.sub.0.1, O.sub.0.4).sub.0.7 - 5% Ni - 3%                   SiO.sub.2 -              1600° C. - 1 hr                                                                 --                                            1.9% Si - 0.1% C                                                           46  90% Ti(N.sub.0.7, O.sub.0.3).sub.0.6 - 4.9% Ni - 5% NiO                                                 1500° C. - 1 hr                                                                 --                                            0.1% C                                                                     47  90% Ti(N.sub.0.7, C.sub.0.1, O.sub.0.2).sub.0.8 - 5% Ni                                                 "       --                                            0.5% ZrO.sub.2 - 4% Zr - 0.5% C                                            48  90% (Ti.sub.0.8, Zr.sub.0.2) (N.sub. 0.8, O.sub.0.2).sub.0.8 - 4% Co           -                        1550° C. - 1 hr                                                                 --                                            4% Ni - 2% Al.sub.2 O.sub.3                                                49  80% Ti(N.sub.0.8, O.sub.0.2).sub.0.70 - 5% ZrN - 5% Ni                                                  1600° C. - 1 hr                                                                 --                                            5% Mo - 5% Al.sub.2 O.sub.3                                                50  80% Ti(N.sub.0.8, O.sub.0.2).sub.0.70 - 9% Al.sub.2 O.sub.3 - 5% Ni                                     "       1200° C. - 3 hrs                       5% Cr - 1% Al                                                              __________________________________________________________________________

                                      TABLE 9                                      __________________________________________________________________________     Mechanical properties                                                          Transverse                                                                     rupture                 Corrosion resistance                                   Sample                                                                             strength                                                                             Hardness      Artificial                                                                               Artificial                                   No. (Kg/mm.sup.2)                                                                        (HRA)                                                                               Tone     sea-water sweat                                        __________________________________________________________________________     43  100   91.2 Gold color                                                                              Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 44  105   90.5 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 45  103   91.0 Reddish light gold                                                                      Not color-changed                                                                        Not color-changed                                           color    nor corroded                                                                             nor corroded                                 46  110   91.2 Light gold color                                                                        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 47  107   90.9 Gold color                                                                              Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 48  105   91.4 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 49  100   91.3 Light gold color                                                                        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 50   95   91.5 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 __________________________________________________________________________

EXAMPLE 6

Each powder of AlN, Si₃ N₄, BN and Mo₂ C and each of the powdery materials used in Example 4 were blended in a predetermined proportion, and were sintered in the same manner as in Example 4. Samples thus obtained were tested for mechanical properties, tone and corrosion resistance. Blend composition, sintering conditions and solid solution treatment conditions of each sample are shown in Table 10, and test results of the mechanical properties, tone and corrosion resistance regarding samples which underwent the sintering treatment and the solid solution treatment are presented in Table 11.

                                      TABLE 10                                     __________________________________________________________________________                                        Solid solution                              Sample                     Sintering                                                                              treatment                                   No. Blend composition (wt. %)                                                                             conditions                                                                             conditions                                  __________________________________________________________________________     51  46% TiN.sub.0.85 - 46% TiO - 6% Ni - 1.5% AlN -                                                       1600° C. - 1 hr                                                                 --                                              0.5% Al                                                                    52  90% Ti(N.sub.0.9, C.sub.0.1).sub.0.75 - 6% Ni - 2% Si.sub.3 N.sub.4                                   "       --                                              2% Mo.sub.2 C                                                              53  90% Ti(N.sub.0.7, O.sub.0.3).sub.0.6 - 5.9% Ni - 2% BN                                                1550° C. - 1 hr                                                                 --                                              2% Mo.sub.2 C - 0.1% C                                                     54  90% Ti(N.sub.0.7, C.sub.0.1, O.sub.0.2).sub.0.8 - 6% Ni - 4%                                          1600° C. - 1 hr                                                                 --                                          55  75% Ti(N.sub.0.7, C.sub.0.1, O.sub.0.2).sub.0.8 - 10% Ni - 5% Cr                                      1500° C. - 1 hr                                                                 --                                              10% Mo.sub.2 C                                                             56  75% Ti(N.sub.0.7, C.sub.0.1, O.sub.0.2).sub.0.8 - 10% Ni                                              "       1200° C. - 3 hrs                         10% Mo.sub.2 C - 2.5% Ti - 2.5% Al                                         57  80% (Ti.sub.0.8, Zr.sub.0.2) (N.sub.0.8, O.sub.0.2).sub.0.8 - 10% Ni           -                      1450° C. - 1 hr                                                                 --                                              5% Co - 4.5% BN - 0.5% C                                                   58  80% (Ti.sub.0.8, V.sub.0.2) N.sub.0.75 - 4% TiO - 10% Ni                                              1500° C. - 1 hr                                                                 1200° C. - 3 hrs                         2% AlN - 2% Al - 2% Ti                                                     59  70% (Ti.sub.0.8, Cr.sub.0.2) (N.sub.0.9, O.sub.0.1).sub.0.8                                           1450° C. - 1 hr                                                                 --                                              10% Ni - 5% Co - 5% Cr - 10 Mo.sub.2 C                                     __________________________________________________________________________

                                      TABLE 11                                     __________________________________________________________________________     Mechanical properties                                                          Transverse                                                                     rupture                 Corrosion resistance                                   Sample                                                                             strength                                                                             Hardness      Artificial                                                                               Artificial                                   No. (Kg/mm.sup.2)                                                                        (HRA)                                                                               Tone     sea-water sweat                                        __________________________________________________________________________     51  110   91.0 Gold color                                                                              Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 52  115   90.8 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 53  105   91.4 Light gold color                                                                        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 54  108   91.5 Gold color                                                                              Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 55  110   90.8 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 56  115   91.2 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 57  107   91.0 "        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 58  113   90.7 Light gold color                                                                        Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 59  117   90.5 Gold color                                                                              Not color-changed                                                                        Not color-changed                                                    nor corroded                                                                             nor corroded                                 __________________________________________________________________________

EXAMPLE 7

Sample Nos. 30, 37 and 42 sintered in Example 4, Sample Nos. 45 and 48 sintered in Example 5, and Sample Nos. 51, 54 and 59 sintered in Example 6 were each subjected to an HIP treatment under conditions of 1500 bar and 1350° C., and were then tested for mechanical properties, tone and corrosion resistance. Obtained test results are shown in Table 12:

                                      TABLE 12                                     __________________________________________________________________________                       Mechanical properties                                                          Transverse                                                                     rupture       Corrosion resistance                           Sample            strength                                                                             Hardness                                                                               Artificial                                                                            Artificial                              No. Sample conditions                                                                            (Kg/mm.sup.2)                                                                        (HRA)                                                                               Tone                                                                              sea-water                                                                             sweat                                   __________________________________________________________________________     60  HIP-treated Sample No. 30                                                                    115   90.9 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                61  HIP-treated Sample No. 37                                                                    120   90.3 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                62  HIP-treated Sample No. 42                                                                    113   91.1 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                63  HIP-treated Sample No. 45                                                                    110   90.9 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                64  HIP-treated Sample No. 48                                                                    113   91.5 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                65  HIP-treated Sample No. 51                                                                    116   91.1 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                66  HIP-treated Sample No. 54                                                                    115   91.4 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                67  HIP-treated Sample No. 59                                                                    123   90.4 Gold                                                                              Not color-                                                                            Not color-                                                           color                                                                             changed nor                                                                           changed nor                                                             corroded                                                                              corroded                                __________________________________________________________________________

EXAMPLE 8

Samples having a size of 6φ×20 mm of the sintered alloy for decoration according to this invention were prepared by sintering compacts each having a blend composition of 85% Ti(N₀.5, O₀.5)₀.78 -10% (Ta₀.3, V₀.7)C-5% Ni (Sample No. 68) and of 75% Ti(N₀.5, O₀.5)₀.78 -20% (Ta₀.3, V₀.7)C-5% Ni (Sample No. 69), in the same manner as in Example 1, respectively.

On the other hand, Referential samples having a size of 6φ×20 mm were prepared by coating TiN, by means of the sputtering process, on the surface of a stainless steel (JIS standard; SUS 304, Sample No. 70) or of a high speed steel (JIS standard; SKH-9, Sample No. 71), or by coating TiN on the surface of a WC-6% Co cemented carbide alloy (Sample No. 72) by means of the chemical deposition process, respectively.

With the mirror-finished peripheral surface of each sample having a diameter of 20 mm was contacted a nylon series fishing line having a size of 1φ×2,000 mm, and part of the fishing line was set so as to be soaked in an artificial sea-water all the time. Then, abrasion resistance and corrosion resistance to the artificial sea-water at the sliding portion, of each sample, were examined by fixing the sample and setting the fishing line in such a manner that the rotating and moving the fishing line is slidden and worn at the contact surface.

The results of the examination and the characteristics of each sample are shown in Table 13.

                                      TABLE 13                                     __________________________________________________________________________                    Wear resistance and corrosion resistance                        Sample                                                                             Hardness   Width of string groove after                                    No. (Hv) Tone  10.sup.5 time sliding                                                                        Corrosion resistance                              __________________________________________________________________________     68  1382 Gold color                                                                           1.5 μm     Good                                              69  1477 Light gold                                                                           1.0 μm     "                                                          color                                                                 70   450 Grayish                                                                              90 μm at 3000 times                                                                       Color-changed                                              white color                                                           71   850 Gold color                                                                           60 μm at 5000 times                                                                       Slightly color-changed                                           and peeled off in                                                              some places                                                     72  1653 Gold color                                                                           1.5 μm and slightly                                                                       Irregular tone                                                   peeled off    produced                                          __________________________________________________________________________

As be definite from the aforementioned results, it has been found that the sintered alloy for decoration according to this invention has together decorativeness suitable for decorative members as well as excellent corrosion resistance and mechanical properties. 

What is claimed is:
 1. A sintered alloy for decoration which consists essentially of:(A) 2 to 30% by weight of a binding phase comprising one or more elements selected from the group consisting of Fe, Ni, Co, Cr, Mo and W; (B) 0 to 10% by weight of a strengthening phase comprising at least one material selected from the group consisting of metal, an alloy, a metal oxide, a metal nitride and a metal carbide; (C) a hard phase represented by the formula:

    (Tia, Mb) (Nw, Cx, Oy)z

wherein M is one or more elements selected from the group consisting of Zr, Hf, V, Nb, Ta and Cr; a is a atomic ratio of Ti; b is an atomic ratio of a metal represented by M; a+b=1; 1≧a≧0.4; 0.6≧b≧0; N is nitrogen; C is carbon; O is oxygen; w, x and y are atomic ratios of nitrogen, carbon and oxygen, respectively; z is a ratio of non-metallic elements with respect to the metals; w+x+y=1; x+y>0; 1≧w≧0.4; 0.15≧x≧0; 0.6≧y≧0; and 0.95≧z≧0.6; and (D) inevitable impurities, wherein said colored sintered alloy (i) is the product of a sintering process that uses, as a starting material, a titanium compound which has a substoichiometric composition, such that nitrogen gas liberated during said sintering process nitrogenizes said titanium compound, and (ii) contains an amount of carbon, calculated with the sum of said strengthening phase and said hard phase taken as 100%, that is no greater than 4.2 atomic %.
 2. A sintered alloy for decoration according to claim 1, wherein said strengthening phase comprises one or more metals selected from the group consisting of P, Al, B, Si, Mn, Ti, Zr, Hf, V, Nb, Ta and one or more alloys thereof.
 3. A sintered alloy for decoration according to claim 1, wherein said strengthening phase comprises one or more oxides selected from the group consisting of Al₂ O₃, Y₂ O₃, ZrO₂, MgO, NiO and SiO₂.
 4. A sintered alloy for decoration according to claim 1, wherein said strengthening phase comprises one or more nitrides or carbides selected from the group consisting of AlN, Si₃ N₄, BN and, Mo₂ C and one or more compounds thereof.
 5. A sintered alloy for decoration according to claim 1, wherein said titanium compound is represented by the formula TiNz, wherein z is as defined in claim
 1. 6. A decorative metal member comprised of a colored sintered alloy consisting essentially of:(A) 2 to 30% by weight of a binding phase comprising one or more elements selected from the group consisting of Fe, Ni, Co, Cr, Mo and W; (B) 0 to 10% by weight of a strengthening phase comprising at least one material selected from the group consisting of metal, an alloy, a metal oxide, a metal nitride and a metal carbide; (C) a hard phase represented by the formula:

    (Tia, Mb) (Nw, Cx, Oy)z

wherein M is one or more elements selected from the group consisting of Zr, Hf, V, Nb, Ta and Cr; a is a atomic ratio of Ti; b is an atomic ratio of a metal represented by M; a+b=1; 1≧a≧0.4; 0.6≧b≧0; N is nitrogen; C is carbon; O is oxygen; w, x and y are atomic ratios of nitrogen, carbon and oxygen, respectively; z is a ratio of non-metallic elements with respect to the metals; w+x+y=1; x+y>0; 1≧w≧0.4; 0.15≧x≧0; 0.6≧y≧0; and 0.95≧z≧0.6; and (D) inevitable impurities, wherein said colored sintered alloy (i) is the product of a sintering process that uses, as a starting material, a titanium compound which has a substoichiometric composition, such that nitrogen gas liberated during said sintering process nitrogenizes said titanium compound, and (ii) contains an amount of carbon, calculated with the sum of said strengthening phase and said hard phase taken as 100%, that is no greater than 4.2 atomic %.
 7. A decorative metal member according to claim 6, wherein said sintered alloy retains a gold color tone.
 8. A decorative metal member according to claim 6, wherein said titanium compound is represented by the formula TiNz, wherein z is as defined in claim
 1. 